U.S. patent application number 14/624906 was filed with the patent office on 2016-08-18 for determining reactive power capability of a renewable energy system.
The applicant listed for this patent is General Electric Company. Invention is credited to Werner Gerhard Barton, Carsten Junge, Arnim Smolenski, Enno Ubben.
Application Number | 20160237990 14/624906 |
Document ID | / |
Family ID | 55446594 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160237990 |
Kind Code |
A1 |
Ubben; Enno ; et
al. |
August 18, 2016 |
DETERMINING REACTIVE POWER CAPABILITY OF A RENEWABLE ENERGY
SYSTEM
Abstract
Systems and methods for controlling a renewable energy system
based on actual reactive power capability of the renewable energy
system are provided. The reactive power output of the renewable
energy system can be controlled based at least in part on an
initial reactive power limit. The initial reactive power limit can
be determined based on rated reactive power for the power
generation units in the renewable energy system. When a difference
between a reactive power demand and the actual reactive power
production of the renewable energy system fall outside a threshold,
the initial reactive power limit can be adjusted to a corrected
reactive power limit that is closer to the actual reactive power
capability of the renewable energy system.
Inventors: |
Ubben; Enno; (Steinfurt,
DE) ; Barton; Werner Gerhard; (Gescher, DE) ;
Junge; Carsten; (Rheine, DE) ; Smolenski; Arnim;
(Lingen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
55446594 |
Appl. No.: |
14/624906 |
Filed: |
February 18, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03D 7/048 20130101;
Y02E 10/723 20130101; H02J 3/382 20130101; Y02E 10/72 20130101;
F03D 7/042 20130101; H02J 2300/20 20200101; F03D 7/047 20130101;
H02P 9/305 20130101; H02J 3/381 20130101; H02J 3/18 20130101; Y02E
40/30 20130101; F03D 7/00 20130101; Y02E 10/763 20130101; Y02E
10/76 20130101; H02J 3/1885 20130101; F03D 9/257 20170201 |
International
Class: |
F03D 9/00 20060101
F03D009/00; H02J 3/18 20060101 H02J003/18; H02P 9/30 20060101
H02P009/30 |
Claims
1. A method for controlling a renewable energy system, comprising:
controlling, by one or more control devices, a reactive power
output for a renewable energy system based at least in part on an
initial reactive power limit for the renewable energy system;
determining, by the one or more control devices, a difference
between a reactive power demand and an actual reactive power
production for the renewable energy system; wherein when the
difference falls outside a threshold, the method comprises:
determining, by the one or more control devices, a correction
factor for the initial reactive power limit; adjusting, by the one
or more control devices, the initial reactive power limit to a
corrected reactive power limit based at least in part on the
correction factor; and controlling, by the one or more control
devices, the reactive power output for the renewable energy system
based at least in part on the corrected reactive power limit;
detecting, by the one or more control devices, the difference
returning to within the threshold; and in response to detecting the
difference returning to within the threshold, controlling, by the
one or more control devices, the reactive power output based at
least in part on the initial reactive power limit.
2. (canceled)
3. The method of claim 1, wherein the initial reactive power limit
is determined by aggregating a rated reactive power for each of a
plurality of power generation units in the renewable energy
system.
4. The method of claim 1, wherein the correction factor results in
adjusting the initial reactive power limit towards the actual
reactive power capability of the renewable energy system.
5. The method of claim 1, wherein the initial reactive power limit
comprises an initial maximum reactive power limit and an initial
minimum reactive power limit.
6. The method of claim 5, wherein the corrected reactive power
limit comprises a corrected maximum reactive power limit and a
corrected minimum reactive power limit.
7. The method of claim 1, wherein the threshold comprises 5% of
rated reactive power for the renewable energy system.
8. The method of claim 1, wherein the corrected reactive power
limit is used to limit a reactive power command for the renewable
energy system.
9. The method of claim 8, wherein the reactive power command is
distributed to a plurality of power generation units.
10. A control system for controlling a renewable energy system, the
control system comprising: a voltage regulator implemented by one
or more control devices, the voltage regulator configured to
provide a reactive power command based at least in part on a
voltage error signal; a limiter implemented by the one or more
control devices, the limiter configured to limit the reactive power
command based at least in part on an initial reactive power limit
for the renewable energy system; a reactive power limit correction
module implemented by the one or more control devices, the reactive
power limit correction module configured to adjust the initial
reactive power limit to a corrected reactive power limit when a
difference between the reactive power command for the renewable
energy system and an actual reactive power production for the
renewable energy system falls outside of a threshold, and wherein
the reactive power limit correction module is configured to detect
the difference returning to within the threshold, and in response
to detecting the difference returning to within the threshold,
control the reactive power output based at least in part on the
initial reactive power limit; wherein the corrected reactive power
limit corrects the initial reactive power limit towards the actual
reactive power capability of the renewable energy system.
11. The control system of claim 10, the initial reactive power
limit is determined by aggregating a rated reactive power for each
of a plurality of power generation units in the renewable energy
system.
12. The control system of claim 10, wherein the threshold comprises
5% of rated reactive power for the renewable energy system.
13. The control system of claim 10, wherein the corrected reactive
power limit is determined based at least in part on a correction
factor, the correction factor determined based on the difference
between the reactive power demand for the renewable energy system
and the actual reactive power production for the renewable energy
system.
14. The control system of claim 10, wherein the reactive power
command is determined based at least in part on a power factor
setpoint for the renewable energy system.
15. A wind farm, comprising: a plurality of wind turbines; a
plurality of wind turbine controllers, each wind turbine controller
associated with at least one of the plurality of wind turbines; and
a wind farm controller, the wind farm controller in communication
with each of the wind turbine controllers, the wind farm controller
configured to adjust an initial reactive power limit to a corrected
reactive power limit based at least in part on a difference between
a reactive power demand for the wind farm and an actual reactive
power production for the wind farm, the wind farm controller
further configured to control the reactive power output for the
wind farm based on the corrected reactive power limit, and wherein
the wind farm controller is configured to detect the difference
returning to within a threshold, and in response to detecting the
difference returning to within the threshold, control the reactive
power output based at least in part on the initial reactive power
limit; wherein the initial reactive power limit is determined by
aggregating a rated reactive power for each of a plurality of wind
turbines in the wind farm and the corrected reactive power limit
adjusts the initial reactive power limit toward an actual reactive
power capability of the wind farm.
16. The wind farm of claim 15, wherein the wind farm controller is
configured to adjust an initial reactive power limit to a corrected
reactive power limit based at least in part on a difference between
a reactive power demand for the wind farm and an actual reactive
power production for the wind farm by determining that the
difference falls outside the threshold and adjusting the initial
reactive power limit to the corrected reactive power limit when the
difference falls outside the threshold.
17. The wind farm of claim 16, wherein the initial reactive power
limit is adjusted to the corrected reactive power limit based at
least in part on a correction factor, the correction factor
determined based on the difference between the reactive power
demand and the actual reactive power production.
18. The wind farm of claim 16, wherein the threshold is 5% of rated
reactive power for the wind farm.
19. The wind farm of claim 15, wherein the wind farm controller is
configured to distribute the reactive power command among the
plurality of wind turbine controllers.
20. The wind farm of claim 15, wherein the wind farm controller is
configured to control the reactive power output of the wind farm
based at least in part on a power factor setpoint.
Description
FIELD OF THE INVENTION
[0001] The present subject matter relates generally to renewable
energy sources, and more particularly, to systems and methods for
determining reactive power capability of renewable energy systems,
such as wind farms, solar farms.
BACKGROUND OF THE INVENTION
[0002] Renewable energy systems, such as wind turbine systems,
solar power systems, energy storage systems, etc., have
increasingly been used for power generation throughout the world.
Renewable energy systems can include a plant or farm having a
plurality of power generation units (e.g. wind turbines) that are
collectively coupled to a utility grid at a point of interconnect.
The renewable energy system can include a control system having a
farm level controller(s) and unit level controller(s) to regulate
the real and reactive power output of the renewable energy
system.
[0003] A renewable energy farm may be required to fulfill a
reactive power capability at the point of interconnect to provide a
desired power factor (e.g. based on a power factor setting). In
some cases, renewable energy systems may be required to have the
capability to provide a rated reactive power capability in a
voltage range of .+-.10% of nominal voltage at the point of
interconnect. To fulfill this requirement, an on-load tap changing
transformer can be required. Including an on-load tap changing
transformer at each power generation unit (e.g. each wind turbine)
can be costly. As an alternative, reactive power capability can be
provided by adjusting active power production of the renewable
energy farm at certain voltage levels (e.g. voltage levels outside
of the .+-.5% of nominal voltage band). However, this can require
knowledge of the actual reactive power limits of the renewable
energy farm.
[0004] The reactive power limit of a renewable energy farm is
typically determined by aggregating the reactive power limits of
individual power generation units in the farm. The reactive power
limit of an individual power generation unit is typically defined
as rated reactive power for the unit and does not change based on
system behavior. In situations wherein individual power generation
units are clamped to voltage limits, the individual power
generation units may not be able to provide rated reactive power,
thus the rate reactive power is not a good estimate of the actual
reactive power limit of the power generation unit.
[0005] Thus, a need exists for determining actual reactive power
limits of a renewable energy farm under various system conditions.
A system and method that can reduce active power production based
on the actual reactive power capability in order to meet a power
factor requirement would be particularly useful.
BRIEF DESCRIPTION OF THE INVENTION
[0006] Aspects and advantages of embodiments of the present
disclosure will be set forth in part in the following description,
or may be learned from the description, or may be learned through
practice of the embodiments.
[0007] One example aspect of the present disclosure is directed to
a method for controlling a renewable energy system, such as a wind
farm, solar farm, or other renewable energy system. The method
includes controlling, by one or more control devices, a reactive
power output for a renewable energy system based at least in part
on an initial reactive power limit for the renewable energy system.
The method further includes determining, by the one or more control
devices, a difference between a reactive power demand and an actual
reactive power production for the renewable energy system. When the
difference falls outside a threshold, the method includes
determining, by the one or more control devices, a correction
factor for the initial reactive power limit and adjusting, by the
one or more control devices, the initial reactive power limit to a
corrected reactive power limit based at least in part on the
correction factor. The method further includes controlling, by the
one or more control devices, the reactive power output for the
renewable energy system based at least in part on the corrected
reactive power limit.
[0008] Another example aspect of the present disclosure is directed
to a control system for controlling a renewable energy system. The
control system includes a voltage regulator implemented by one or
more control devices. The voltage regulator is configured to
provide a reactive power command based at least in part on a
voltage error signal. The control system can further include a
limiter implemented by the one or more control devices. The limiter
is configured to limit the reactive power command based at least in
part on an initial reactive power limit for the renewable energy
system. The control system further includes a reactive power limit
correction module implemented by the one or more control devices.
The reactive power limit correction module is configured to adjust
the initial reactive power limit to a corrected reactive power
limit when a difference between the reactive power command for the
renewable energy system and an actual reactive power production for
the renewable energy system falls outside of a threshold. The
corrected reactive power limit corrects the initial reactive power
limit towards the actual reactive power capability of the renewable
energy system.
[0009] Yet another example aspect of the present disclosure is
directed to a wind farm. The wind farm includes a plurality of wind
turbines and a plurality of wind turbine controllers. Each wind
turbine controller is associated with at least one of the plurality
of wind turbines. The wind farm further includes a wind farm
controller. The wind farm controller is in communication with each
of the wind turbine controllers. The wind farm controller is
configured to adjust an initial reactive power limit to a corrected
reactive power limit based at least in part on a difference between
a reactive power demand for the wind farm and an actual reactive
power production for the wind farm. The wind farm controller is
further configured to control the reactive power output of the wind
farm based on the corrected reactive power limit. The initial
reactive power limit is determined by aggregating a rated reactive
power for each of a plurality of wind turbines in the wind farm and
the corrected reactive power limit adjusts the initial reactive
power limit toward the actual reactive power capability of the wind
farm.
[0010] Variations and modifications can be made to these example
aspects of the present disclosure.
[0011] These and other features, aspects and advantages of various
embodiments will become better understood with reference to the
following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the present disclosure
and, together with the description, serve to explain the related
principles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Detailed discussion of embodiments directed to one of
ordinary skill in the art are set forth in the specification, which
makes reference to the appended figures, in which:
[0013] FIG. 1 depicts an example wind turbine that can be
controlled according to example aspects of the present
disclosure;
[0014] FIG. 2 depicts an example controller according to example
aspects of the present disclosure;
[0015] FIG. 3 depicts an example wind farm according to example
aspects of the present disclosure;
[0016] FIG. 4 depict an example control topology for a wind farm
according to example aspects of the present disclosure;
[0017] FIG. 5 depicts an example control topology for determining a
corrected maximum reactive power limit according to example aspects
of the present disclosure;
[0018] FIG. 6 depicts an example control topology for determining a
corrected minimum reactive power limit according to example aspects
of the present disclosure;
[0019] FIG. 7 depicts a graphical representation of example
behavior of a control system according to example aspects of the
present disclosure; and
[0020] FIG. 8 depicts a flow diagram of an example method for
controlling a wind farm according to example aspects of the present
disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment can be used with
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0022] Example aspects of the present disclosure are directed to
systems and methods for determining reactive power capability for
renewable energy systems to provide corrected reactive power limits
in controlling reactive power output. A renewable energy system can
include a farm or plant level control system for regulating
voltage, reactive power, and/or power factor at the renewable
energy system level. For instance, the farm level control system
can include an inner loop voltage regulator with an outer loop
reactive power/power factor regulator. The voltage regulator can
compute reactive power commands based at least in part on the
reactive power limits of the renewable energy system. The reactive
power commands can then be distributed to individual power
generation units (e.g. using a proportional distribution
algorithm).
[0023] At the individual power generation units, a controller(s)
can include an inner loop voltage regulator that can determine, for
instance, commands for controlling the individual power generation
unit. The input to the voltage regulator can include a reactive
power regulator regulating the reactive power of the power
generation unit based on the reactive power command distributed to
the individual power generation unit. The reactive power regulator
can provide a voltage reference to the inner loop voltage
regulator. The reference can be clamped to the voltage limits of
the power generation unit (e.g. .+-.10% of nominal voltage of the
power generation unit).
[0024] The controller(s) associated with the individual power
generation units can provide feedback data to the farm level
control system. The feedback can include signals indicative of
actual reactive power output by the individual power generation
unit, minimum reactive power limit for the power generation unit,
and maximum power limit for the power generation unit. These
feedback signals can be aggregated to generate a farm or plant
level aggregation signal for actual reactive power output, minimum
reactive power limit, and maximum reactive power limit. The
aggregated maximum reactive power limit and minimum reactive power
limit can be used to clamp reactive power commands generated by the
farm level control system.
[0025] According to example aspects of the present disclosure, a
reactive power limit determined for the renewable energy system can
be adjusted from an initial reactive power limit (e.g. determined
based on rated reactive power) to reflect the actual reactive power
capability of the renewable energy system based on current
operating conditions. More particularly, in the event a difference
between a reactive power demand and the actual reactive power
production exceeds a threshold (e.g. greater than 5% of rated
reactive power), the control system can adjust the reactive power
limits towards the actual reactive power production of the
renewable energy system. The renewable energy system can then be
controlled in accordance with the corrected reactive power limits,
for instance, by clamping the reactive power command closer to be
closer to within the actual reactive power capability of the
renewable energy system.
[0026] The corrected reactive power limits can be dynamically
adjusted during operation based on the magnitude of the difference
between the reactive power demand and the actual reactive power
production. Once the difference between the reactive power command
and the actual reactive power production returns to within a
threshold and/or the voltage of the renewable energy system is able
to follow a voltage reference generated from the reactive power
regulator in the farm level control system, the reactive power
limits can be adjusted back to their initial values.
[0027] Adjusting the reactive power limits according to example
aspects of the present disclosure can allow for improved control of
the renewable energy system to meet reactive power demands. For
instance, a renewable energy system can be controlled based at
least in part on the corrected reactive power limits to provide a
rated reactive power capability in a voltage range of .+-.10% of
nominal voltage at the point of interconnect. More particularly,
the corrected reactive power limits can be used to reduce the
active power production of the renewable energy system at certain
voltage levels (e.g. voltage levels outside of the .+-.5% of
nominal voltage band) to meet a power factor demand. In this way,
rated reactive power can be provided under various grid conditions
without requiring, for instance, an on-load tap changing
transformer.
[0028] Referring now to the drawings, example embodiments of the
present disclosure will be discussed in detail. Aspects of the
present disclosure will be discussed with reference to wind
renewable energy systems for purposes of illustration and
discussion. Those of ordinary skill in the art, using the
disclosures provided herein, will understand that example aspects
of the present disclosure can be implemented in other power
generation systems, such as solar farms, energy storage systems,
etc.
[0029] FIG. 1 illustrates a perspective view of one embodiment of a
wind turbine 10. As shown, the wind turbine 10 generally includes a
tower 12 extending from a support surface 14, a nacelle 16 mounted
on the tower 12, and a rotor 18 coupled to the nacelle 16. The
rotor 18 includes a rotatable hub 20 and at least one rotor blade
22 coupled to and extending outwardly from the hub 20. For example,
in the illustrated embodiment, the rotor 18 includes three rotor
blades 22. However, in an alternative embodiment, the rotor 18 may
include more or less than three rotor blades 22. Each rotor blade
22 may be spaced about the hub 20 to facilitate rotating the rotor
18 to enable kinetic energy to be transferred from the wind into
usable mechanical energy, and subsequently, electrical energy. For
instance, the hub 20 may be rotatably coupled to an electric
generator (not shown) positioned within the nacelle 16 to permit
electrical energy to be produced.
[0030] The wind turbine 10 may also include a wind turbine
controller 26 centralized within the nacelle 16. However, in other
embodiments, the controller 26 may be located within any other
component of the wind turbine 10 or at a location outside the wind
turbine. Further, the controller 26 may be communicatively coupled
to any number of the components of the wind turbine 10 in order to
control the operation of such components and/or to implement a
control action. As such, the controller 26 may include a computer
or other suitable processing unit. Thus, in several embodiments,
the controller 26 may include suitable computer-readable
instructions that, when implemented, configure the controller 26 to
perform various different functions, such as receiving,
transmitting and/or executing wind turbine control signals.
[0031] Referring now to FIG. 2, a block diagram of one embodiment
of suitable components that may be included within the controller
26 is illustrated in accordance with aspects of the present
disclosure. As shown, the controller 26 may include one or more
processor(s) 58 and associated memory device(s) 60 configured to
perform a variety of computer-implemented functions (e.g.,
performing the methods, steps, calculations and the like disclosed
herein). As used herein, the term "processor" refers not only to
integrated circuits referred to in the art as being included in a
computer, but also refers to a controller, a microcontroller, a
microcomputer, a programmable logic controller (PLC), an
application specific integrated circuit, application-specific
processors, digital signal processors (DSPs), Application Specific
Integrated Circuits (ASICs), Field Programmable Gate Arrays
(FPGAs), and/or any other programmable circuits. Further, the
memory device(s) 60 may generally include memory element(s)
including, but are not limited to, computer readable medium (e.g.,
random access memory (RAM)), computer readable non-volatile medium
(e.g., a flash memory), one or more hard disk drives, a floppy
disk, a compact disc-read only memory (CD-ROM), compact
disk-read/write (CD-R/W) drives, a magneto-optical disk (MOD), a
digital versatile disc (DVD), flash drives, optical drives,
solid-state storage devices, and/or other suitable memory
elements.
[0032] Additionally, the controller 26 may also include a
communications module 62 to facilitate communications between the
controller 26 and the various components of the wind turbine 10.
For instance, the communications module 62 may include a sensor
interface 64 (e.g., one or more analog-to-digital converters) to
permit the signals transmitted by one or more sensors 65, 66, 67 to
be converted into signals that can be understood and processed by
the controller 26. Furthermore, it should be appreciated that the
sensors 65, 66, 67 may be communicatively coupled to the
communications module 62 using any suitable means. For example, as
shown in FIG. 2, the sensors 65, 66, 67 are coupled to the sensor
interface 64 via a wired connection. However, in alternative
embodiments, the sensors 65, 66, 67 may be coupled to the sensor
interface 64 via a wireless connection, such as by using any
suitable wireless communications protocol known in the art. For
example, the communications module 62 may include the Internet, a
local area network (LAN), wireless local area networks (WLAN), wide
area networks (WAN) such as Worldwide Interoperability for
Microwave Access (WiMax) networks, satellite networks, cellular
networks, sensor networks, ad hoc networks, and/or short-range
networks. As such, the processor 58 may be configured to receive
one or more signals from the sensors 65, 66, 67.
[0033] The sensors 65, 66, 67 may be any suitable sensors
configured to measure any operating data points of the wind turbine
10 and/or wind parameters of the wind farm. It should also be
understood that any other number or type of sensors may be employed
and at any location. For example, the sensors may be
accelerometers, pressure sensors, strain gauges, angle of attack
sensors, vibration sensors, MIMU sensors, camera systems, fiber
optic systems, anemometers, wind vanes, Sonic Detection and Ranging
(SODAR) sensors, infra lasers, Light Detecting and Ranging (LIDAR)
sensors, radiometers, pitot tubes, rawinsondes, other optical
sensors, and/or any other suitable sensors. It should be
appreciated that, as used herein, the term "monitor" and variations
thereof indicates that the various sensors of the wind turbine 10
may be configured to provide a direct measurement of the parameters
being monitored or an indirect measurement of such parameters.
Thus, the sensors 65, 66, 67 may, for example, be used to generate
signals relating to the parameter being monitored, which can then
be utilized by the controller 26 to determine the actual
condition.
[0034] Referring now to FIG. 3, a wind farm 200 that is controlled
according to example aspects of the present disclosure is
illustrated. As shown, the wind farm 200 may include a plurality of
wind turbines 202, including the wind turbine 10 described above,
and a farm controller 222. For example, as shown in the illustrated
embodiment, the wind farm 200 includes twelve wind turbines,
including wind turbine 10. However, in other embodiments, the wind
farm 200 may include any other number of wind turbines, such as
less than twelve wind turbines or greater than twelve wind
turbines. In one embodiment, the controller 26 of the wind turbine
10 may be communicatively coupled to the farm controller 222
through a wired connection, such as by connecting the controller 26
through suitable communicative links 226 (e.g., a suitable cable).
Alternatively, the controller 26 may be communicatively coupled to
the farm controller 222 through a wireless connection, such as by
using any suitable wireless communications protocol known in the
art. In addition, the farm controller 222 may be generally
configured similar to the controllers 26 for each of the individual
wind turbines 202 within the wind farm 200.
[0035] FIG. 4 depicts an example control topology for controlling a
wind farm according to example embodiments of the present
disclosure. The control topology can be implemented using one or
more control devices, such the farm controller 222 and various
individual controllers 26 associated with the individual wind
turbines in the farm 200 shown in FIG. 3.
[0036] As shown in FIG. 4, the one or more control devices can
implement an inner loop voltage regulator 310 for the wind farm and
an outer loop power factor/reactive power regulator 320 for the
wind farm. The voltage regulator 310 can receive a V.sub.REF
command determined from a voltage setpoint and/or an output 322 of
the reactive power regulator 320.
[0037] The reactive power regulator 320 can generate an output 322
based on an error between a clamped Q.sub.REF command and a
Q.sub.ACT signal indicative of the actual reactive power output of
the wind farm. The Q.sub.REF command can be clamped based on an
upper reactive power limit 324 for the wind farm and a lower
reactive power limit for the wind farm 326. The Q.sub.REF command
can be determined from a reactive power (VAR) setpoint and/or a
power factor setpoint. For instance, the Q.sub.REF command can be
determined as tan (pf) *P where pf is the power factor setpoint and
P is the measured power output P.sub.meas of the wind farm.
[0038] The voltage regulator 310 can receive V.sub.REF after it has
been clamped by a voltage maximum 312 for the wind farm and a
voltage minimum 324 for the wind farm. The voltage regulator 310
generates a reactive power command 315 based on the clamped
V.sub.REF signal. The reactive power command 315 can be clamped by
a limiter based on a maximum reactive power limit 330 and a minimum
reactive power limit 340 to generate a clamped reactive power
command Q.sub.CMD. As will be discussed in more detail below, the
maximum reactive power limit 330 and the minimum reactive power
limit 340 can be adjusted from an initial value (e.g. determined
based on rated reactive power) to a corrected value that more
accurately reflects the wind farm reactive power capability in
various operating circumstances.
[0039] The clamped reactive power command Q.sub.REF can be
distributed to controller(s) associated with individual wind
turbines according to a proportional distribution algorithm 350.
For instance, the clamped reactive power command Q.sub.REF can be
distributed to controller(s) 360.1, 360.2 . . . 360.n associated
with the individual wind turbine controllers. As shown, the
reactive power command for each wind turbine can be clamped based
on a maximum reactive power limit 362 for the wind turbine and a
minimum reactive power limit 364 for the wind turbine. The maximum
reactive power limit 362 and minimum reactive power limit 364 can
be determined based on the rated reactive power for the wind
turbine. The clamped reactive power command for the wind turbine
can be compared to a signal indicative of actual reactive power
production 365 for the wind turbine to generate an error signal.
The error signal can be provided to a reactive power regulator
which can generate a voltage command based on the error signal. The
voltage command can be compared to a signal 367 indicative of
actual voltage at the wind turbine to generate an error signal for
a regulator 368 that generates an imaginary current command for the
turbine.
[0040] As shown in FIG. 4, the controller(s) 360.1, 360.2, . . .
360.n can provide various feedback signals for use by the control
system. For instance, a signal indicative of maximum reactive power
limit 362, minimum reactive power limit 364, and actual reactive
power production 365, for each of the wind turbines can be provided
by the controller(s) 360.1, 360.2, . . . 360.n. The signals 365
indicative of actual reactive power production can be aggregated at
370 to generate a signal 325 indicative of actual power production
for the wind farm. The signals 362 indicative of maximum reactive
power limit for each wind turbine can be aggregated at 372 to
generate signal 330 indicative of the maximum reactive power limit
for the wind farm. The signals 364 indicative of the minimum
reactive power limit for each wind turbine can be aggregated at 374
to generate signal 340 indicative of the minimum reactive power
limit for the wind farm.
[0041] As shown, the signals 330 and 340 are used to clamp the
reactive power command 315 output by the voltage regulator 310 to
generate a clamped reactive power command Q.sub.CMD. According to
example aspects of the present disclosure, the signals 330 and 340
can be adjusted from initial values to corrected values during
certain operating conditions. For instance, if a difference between
the reactive power command and the actual reactive power production
of the farm falls outside of a threshold (e.g. greater or less than
5% of rated reactive power relative to the reactive power demand),
the maximum reactive power limit 330 and the minimum reactive power
limit 340 can be adjusted towards the actual reactive power
production of the farm until the difference returns to within the
threshold.
[0042] FIG. 5 depicts a control scheme for an example reactive
power limit correction module implemented by one or more control
devices for adjusting the maximum reactive power limit 330
according to example embodiments of the present disclosure. As
shown, a threshold signal 404 can be generated based on a
percentage of rated reactive power 402 for the wind farm. In the
example of FIG. 5, the threshold signal 404 is representative of 5%
of rated reactive power 402. Other suitable percentages of rated
reactive power can be used without deviating from the scope of the
present disclosure. At 406, a difference between the reactive power
command Q.sub.CMD, the actual reactive power production 325, and
the threshold signal 402 can be determined to generate difference
signal 408.
[0043] A ratio of the difference signal 408 to the rated reactive
power 402 can be determined at 410 and can be provided to
correction factor module 412. The correction factor module 412 can
determine a correction factor 430 for the maximum reactive power
limit 330 based on the ratio of the difference signal 408 to the
rated reactive power 402. For instance, in particular embodiments,
the greater the difference signal 408 relative to rated reactive
power 402, the greater the correction factor 430.
[0044] The correction factor 430 can be used to adjust the maximum
reactive power limit 330 towards the actual reactive power
capability of the wind farm. For instance, the maximum reactive
power limit 330, the correction factor 430 and the actual reactive
power production 325 can be provided to an estimator module 335.
The estimator module 335 can adjust the maximum reactive power
limit 330 towards the actual reactive power production 325 based on
the correction factor 430 to generate an adjusted reactive power
limit 330'. For example, as the correction factor 430 increases,
the adjusted maximum reactive power limit 330' can be adjusted
closer to the actual reactive power production 325. As the
correction factor 430 decreases, the adjusted maximum reactive
power limit 330' can be adjusted closer to the initial maximum
reactive power limit 330.
[0045] FIG. 6 depicts a control scheme for an example reactive
power limit correction module implemented by one or more control
devices for adjusting the minimum reactive power limit 330
according to example embodiments of the present disclosure. As
shown, a threshold signal 402 can be generated based on a
percentage of rated reactive power 402 for the wind farm. In the
example of FIG. 6, the threshold signal 402 is representative of 5%
of rated reactive power 402. At 406, a difference between the
reactive power command Q.sub.CMD, the actual reactive power
production 325, and the threshold signal 402 can be determined to
generate difference signal 408.
[0046] A ratio of the difference signal 408 to the rated reactive
power 402 can be determined at 410 and can be provided to
correction factor module 422. The correction factor module 422 can
determine a correction factor 430 for the minimum reactive power
limit 340 based on the ratio of the difference signal 408 to the
rated reactive power 402. For instance, in particular embodiments,
the greater the difference signal 408 relative to rated reactive
power 402, the greater the correction factor 440.
[0047] The correction factor 440 can be used to adjust the minimum
reactive power limit 340 towards the actual reactive power
capability of the wind farm. For instance, the minimum reactive
power limit 340, the correction factor 440 and the actual reactive
power production 325 can be provided to an estimator module 345.
The estimator module 345 can adjust the minimum reactive power
limit 340 towards the actual reactive power production 325 based on
the correction factor 440 to generate an adjusted reactive power
limit 340'. For example, as the correction factor 440 increases,
the adjusted maximum reactive power limit 340' can be adjusted
closer to the actual reactive power production 325. As the
correction factor 440 decreases, the adjusted maximum reactive
power limit 340' can be adjusted closer to the initial maximum
reactive power limit 330.
[0048] Referring back to FIG. 4, the adjusted maximum reactive
power limit 330' and the adjusted minimum reactive power limit 340'
can be used by a limiter to clamp the output 315 of the voltage
regulator 310 to generate a new reactive power command Q.sub.CMD
that more closely follows the actual reactive power capability of
the wind farm.
[0049] FIG. 7 depicts a graphical representation of the example
behavior of a control system based on reduction of actual reactive
power capability due to a voltage clamp at the individual wind
turbines. FIG. 7 plots time along the horizontal axis and magnitude
of reactive power along the vertical axis. Signal 500 represents
the reduction of actual reactive power capability over time for a
wind farm due to a voltage clamp at the individual wind turbines.
More particularly, at time t30 the actual reactive power capability
reduces to about 7000 kvar. The reactive power setpoint for the
farm Q.sub.SETPOINT remains at 8000 kvar. As shown, Q.sub.CMD
starts increasing to attempt to achieve the reactive power
production specified by Q.sub.SETPOINT. According to example
aspects of the present disclosure, the control system generates a
correction factor to reduce signal 330 indicative of maximum
reactive power limit to an adjusted maximum reactive power limit
330' representative of the actual reactive power capability of the
system. As shown, signal 330' more closely follows signal 500
indicative of the actual reactive power capability of the
system.
[0050] At time t114, the setpoint Q.sub.SETPOINT is reduced to 5000
kvar, while the real reactive power capability 500 is above the
setpoint at 7000 kvar. As shown, the regulator reduces Q.sub.CMD to
follow the setpoint. This causes the difference between the
reactive power command Q.sub.CMD and the actual reactive power
capability 500 to be reduced. As a result, the correction factor
for adjusting the maximum reactive power limit is reduced such that
the adjusted reactive power limit 330' moves back towards the
initial maximum reactive power limit 300.
[0051] FIG. 8 depicts a flow diagram of an example method (600) for
controlling a renewable energy system according to example aspects
of the present disclosure. The method (600) can be implemented by
one or more control devices, such as any of example the control
devices set forth in the present disclosure. In addition, FIG. 8
depicts steps performed in a particular order for purposes of
illustration and discussion. Those of ordinary skill in the art,
using the disclosures provided herein, will understand that various
steps of any of the methods disclosed herein can be modified,
adapted, expanded, omitted, and/or rearranged in various ways
without deviating from the scope of the present disclosure.
[0052] At (602), the method includes controlling a reactive power
output based on an initial reactive power limit. For instance, as
shown in FIG. 4, a reactive power command output by a voltage
regulator 310 can be limited based at least in part on an initial
maximum reactive power limit 330 and/or an initial minimum reactive
power limit 340 to generate reactive power command Q.sub.CMD. The
initial reactive power limit can be determined, for instance, based
at least in part on the rated reactive power of the individual
power generation units. For instance, the initial reactive power
limit can be determined by aggregating a rated reactive power for
each of a plurality of power generation units in the renewable
energy system
[0053] At (604), the method includes determining a difference
between a reactive power demand (e.g. as represented by a reactive
power command) and an actual reactive power production for the
renewable energy system. For instance, a difference between the
Q.sub.CMD and the signal 325 indicative of actual reactive power
production can be determined.
[0054] At (606), the difference can be compared to a threshold. The
threshold can be, for instance, 5% of rated reactive power for the
renewable energy system. When the difference is within threshold,
the method continues to control the reactive power output of the
renewable energy system based on the initial reactive power limit.
When the difference is outside of the threshold, the method
determines a correction factor for the initial reactive power limit
(608). The correction factor can be used to adjust the initial
reactive power limit toward the actual reactive power production of
the renewable energy system. In embodiments, the correction factor
can be determined based on the magnitude of the difference between
the reactive power demand and the actual reactive power production
of the renewable energy system.
[0055] At (610), the reactive power limits are adjusted based on
the correction factor. For instance, the reactive power limits can
be adjusted to a corrected reactive power limit. The corrected
reactive power limit can be closer to the actual reactive power
capability of the renewable energy system. The correction factor
can be used to generate a corrected maximum reactive power limit
and/or a corrected minimum reactive power limit
[0056] At (612), the method includes controlling the reactive power
output based at least in part on the corrected reactive power
limit. For instance, a reactive power command output by a voltage
regulator 310 can be limited based at least in part on the
corrected maximum reactive power limit 330' and/or the corrected
minimum reactive power limit 340' to generate reactive power
command Q.sub.CMD.
[0057] At (614), the difference between the reactive power demand
(as determined based on the corrected reactive power limits) and
the actual reactive power production can be determined. At (616),
it can be determined whether the difference is within a threshold
(e.g. 5% of rated reactive power for the renewable energy system).
If the difference is not within the threshold, the method can
continue to adjust the initial reactive power limits based on a
correction factor as illustrated in FIG. 8. If the difference has
returned to within the threshold, the method can control the
reactive power output based on the initial reactive power limit
(602).
[0058] Although specific features of various embodiments may be
shown in some drawings and not in others, this is for convenience
only. In accordance with the principles of the present disclosure,
any feature of a drawing may be referenced and/or claimed in
combination with any feature of any other drawing.
[0059] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they include structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *